1. Field of the Invention
This invention relates to solar collectors and more particularly to a new and improved solar collector having component parts of low k value (thermal conductivity BTU/hr/FT Sq/.degree.F./in) and multiple glazings.
2. Description of the Prior Art
Prior art solar collectors suffer from a high k value since generally aluminum or stainless steel is used as the frame structure. When dual glazings are used for high efficency, the inner glazing is generally supported independently and spaced from the outer glazing. This increases the gross depth of the frame. An increase in frame depth decreases the value of dual glazing due to increased radiation loss caused by increased mass in the frame structure. Additionally, shadow effect on the absorber plate due to increased height above the absorber causes solar insolation loss. It will be appreciated that the loss due to shadows on the absorber plate is greater than the simple geometrical loss of solar insolation, since forced circulation of fluid into the shaded region of the plate continues to deliver heat to this cooler portion, resulting in a negative contribution to net energy delivered.
The publication entitled "TEFLON SOLAR FILM for Solar Collectors" by DU PONT identified as E-21605 8/78, disclosed TEFLON as an inner glazing with an outer glazing of Lucite acrylic, TEDLAR PVF, or glass. The outer glazing was substantially flat and the inner glazing of TEFLON was independently suspended and spaced from the outer glazing and absorber thereby requiring an increased depth of the frame. The DU PONT publication further disclosed a 1% stretch applied during installation is recommended and will reduce sag during stagnation. And that sag does not generally affect the performance of the collector since the TEFLON film does not stick to the collector plate (absorber) and reestablishes its original position when the plate is cooled to normal use temperature. The DU PONT publication further disclosed several methods for stretching the TEFLON film to remove wrinkles as well as use of a tenter frame to stretch and reduce wrinkles.
The present invention meets the need for an improved flatplate solar collector in that it has the advantages of low k value by use of plastic materials for the housing in lieu of a metal frame. As a further advantage, it is designed to provide a dual glazing for the collector with a minimal increase in gross frame depth thereby minimizing shadow loss and it is designed for the facile and economical installation of film material as the inner glazing.